In today's rapidly advancing semiconductor manufacturing industry, chemical mechanical polishing (CMP) is an advantageous and favored way of planarizing and polishing semiconductor substrates to remove excess materials from over a surface of the semiconductor substrate. In this manner, damascene techniques may be used to form conductive features within openings such as trenches, vias or contacts formed in insulating layers. In damascene processing, a bulk material such as a conductive material is formed over an insulating layer and within such openings formed within the insulating layer, then removed from over the top surface of the insulating layer using chemical mechanical polishing. The resulting structure includes the conductive materials filling the various openings and extending up to the top surface of the insulating layer after the excess conductive materials have been removed from over the top of the insulating layer.
Chemical mechanical polishing involves a polishing pad and includes mechanical and chemical components. The polishing pad rotates and the wafer surface desired to be polished is brought into contact with the rotating polishing pad at a wafer polishing location. The wafer also rotates to enhance polishing. At a second, dispense, location, a dispenser head dispenses a polishing slurry onto the polishing pad. It is desired for the slurry, dispensed onto the polishing pad at the dispense location, to be delivered uniformly to the wafer polishing location so that the polishing pad has a uniform distribution of slurry thereon at the wafer polishing location.
The polishing slurry is a liquid containing a suspended abrasive component and various chemicals. The mechanical aspect of chemical mechanical polishing (CMP) is the physical abrasion of the semiconductor substrate surface by contact with the polishing pad and the abrasives in the slurry. The chemical component includes one or more chemicals in the slurry that selectively react with the material being removed by CMP. It is clearly critical that the slurry dispensed onto the polishing pad is delivered to the wafer polishing location of the polishing pad, i.e. it is important that the slurry, dispensed at a dispense location, does not spin off the polishing pad such that it never reaches the location where the wafer is being polished. This would be an ineffective usage of the slurry and would significantly decrease the polishing efficiency of the CMP tool. Furthermore, if the slurry is not continuously delivered to the entire wafer polishing location, problems such as a poor polishing profile (non-uniformity) within a wafer and wafer-to-wafer polishing inconsistencies, can ensue.
One challenging aspect of the rapidly advancing semiconductor manufacturing industry is that wafer sizes continue to increase. Many CMP tools that were designed for wafers having diameters of 300 mm are now being used to process wafers that have greater diameters such as diameters of 450 millimeters. As a first matter, it is a general principle that within-wafer and wafer-to-wafer uniformity for 450 mm wafers is more difficult to achieve than for smaller wafer sizes. As a second matter, conventional CMP tools have a fixed slurry dispenser head that may not be able to deliver the slurry to the wafer polishing location on the polishing pad using desirable polishing parameters such as the spin speed of the polishing pad. As a third matter, larger polishing pads are typically used for larger wafers, i.e., a larger polishing pad is advantageously used for a 450 mm wafer than a 300 mm wafer, further changing the dynamics of slurry delivery.
FIGS. 1A and 1B show top and side views, respectively, of aspects of a conventional CMP polishing tool. Polishing pad 1 includes grooves 3 within polishing surface 15 and rotates along direction indicated by arrow 5. Fixed dispenser arm 7 includes a dispenser head 11 at dispense location 9.
FIGS. 2A and 2B illustrate some shortcomings of conventional CMP polishing tools. FIG. 2A shows polishing pad 1 with polishing surface 15 rotating in direction 5 and shows slurry 21 dispensed from dispenser head 7 at dispense location 9. In the arrangement illustrated in FIG. 2A, polishing pad 1 includes a first diameter and includes wafer 19 having a diameter of 300 millimeters positioned on polishing pad 1. Polishing pad 1 may include a diameter of about 725-775 mm in the illustrated example. In the arrangement illustrated in FIG. 2A, it can be seen that slurry 21 is successfully delivered to the polishing location of wafer 19. When a larger pad is used in the same CMP tool having the same dispenser arm, the undesirable result is illustrated in FIG. 2B.
In FIG. 2B, the same CMP tool as in FIG. 2A, with the same dispenser arm is used for polishing a larger substrate. Larger wafer 20 may be a semiconductor wafer having a diameter of about 450 millimeters. In order to accommodate the larger substrate size, larger polishing pad 2 is used. Larger polishing pad 2 may include a diameter of about 900 mm to about 1100 mm. Larger polishing pad 2 also rotates along the direction indicated by arrow 5 and it can be seen that very little slurry 21 dispensed from dispense location 9 of dispenser arm 7 reaches the location of larger wafer 20 on larger polishing pad 2. In this example, slurry 21 is whisked off larger polishing pad 2 due to rotation, before reaching the portion of polishing pad 2 where larger wafer 20 is being polished and this will necessarily result in non-uniformities in the polishing rate across larger wafer 20. As such, when a wafer size is increased from 300 mm to 450 mm and the polishing pad is increased in size correspondingly, if the same slurry dispense location is maintained, the slurry dispense would not be effective due to poor distribution of slurry on the polishing pad. Much of slurry 21 is wasted and is expelled off of the polishing pad before slurry 21 reaches the wafer.
With the cost of CMP tools being excessive, it would be economically undesirable to have dedicated CMP tools for various substrate sizes and polishing pad sizes.
It would therefore be desirable to address the above-identified shortcomings and limitations of conventional CMP polishing operations and tools.